Determination of sorbic acid diffusivity in model food gels

The diffusional behaviour of sorbic acid in model food gels is discussed. The apparent diffusivity (Da) of sorbic acid in a aqueous gel containing 1.5%w/w agar, when determined by monodimensional diffusion (infinite gel columns) was found to be 8.8, 8.9 or 9.2 × 10−10 m2/sec at 25°C depending on the method of calculation (eye fitting, eye fitting graphical method or computerized fitting method) and 8.7 × 10−1 m2/sec when determined by tridimensional diffusion (gel cubes immersed into an appropriate solution). The two methods displayed a good agreement; the tridimensional diffusion method had slightly worse repeatability than the monodimensional method (coefficient of variation 10% instead of 5.5% for the infinite gel columns) but has the advantage of being simple and rapid (1‐3 hr instead of 24 hr). For the tridimensional diffusion method, Da values of sorbic acid measured by inward and outward diffusion in gel cubes of different compositions were found to be not significantly different, which suggests an absence of partition effects between the immersion solution and the gel. D a values appear to be slightly dependent on the gelling agent concentration (1.5, 2.5 and 4% w/w agar) in gel containing 40% w/w glycerol and 60% water. Da values of sorbic acid decreased when the temperature decreased. An apparent activation energy of 18 KJ/mol was found for the diffusion of sorbic acid. This value was similar to the activation energy for the change in viscosity of the solution occluded in the gel network. Da values were influenced by the concentration of the diffusant, with a slight decrease when initial concentration of sorbic acid increased, following a linear relationship. The product D.η when η is the viscosity of the solution occluded in the gel was approximately constant.